1. Field of the Invention
This invention relates to a method of controlling the temperature of a cylinder for an extruder (hereinafter referred to as "a cylinder temperature controlling method", when applicable), and a device for practicing the method, and more particularly to a novel improvement of a cylinder assembly which is made up of a plurality of cylinder blocks.
2. Related Art
In general, a twin-screw extruder has a wide range of applications, and therefore its cylinder is divided into a plurality of blocks 3 to 3.5D in cylinder length (where D is the diameter of the screws inserted therein). Depending on the purpose of the extruder, a predetermined number of block cylinders are connected to one another to form a cylinder assembly having a necessary length. In addition, a variety of segment screws different in configuration are provided for the cylinder assembly, so that the latter can be designed relatively freely.
The arrangement of a twin-screw extruder using the above-described cylinder assembly is shown in FIG. 8. In FIG. 8, reference numeral 1 designates a driving device for the twin-screw extruder. As shown in FIG. 8, a cylinder assembly 3 is formed by first through fifth block cylinders 3a through 3e which are laid horizontally and connected to one another with four tie bars 2 (only two tie bars shown in FIG. 8) which extend from the driving device 1 through through-holes formed in the block cylinders 3a through 3e. The first through fifth block cylinders 3a through 3e are controlled in temperature by first through fifth heaters 4a through 4e, respectively. Twin screws 5 are rotatably provided in the cylinder assembly 3.
In the cylinder assembly 3, the block cylinders 3a through 3e are most suitably controlled in temperature by the heaters 4a through 4e, respectively. A resin material supplied through a raw material supply port 6 is moved forward while being molten and kneaded by the screws 5, and finally extruded through a die (not shown). On the other hand, FIG. 6 shows a cylinder assembly comprising flanged block cylinders 3b through 3d each of which has flange-shaped coupling ends. In this case, the flanges of the block cylinders are secured to one another with bolts and nuts to form the cylinder assembly.
The conventional method of controlling the temperature of the cylinder assembly which is formed by coupling the block cylinders to one another, and the conventional device for practicing the method, being designed as described above, involve the following problems: That is, resin material is mixed with a variety of raw materials to form complicated compound materials, and a process of melting thermoplastic resin, and a process of kneading and dispersing compound materials or the like are intricate, and therefore it is difficult to theorize those processes by experiment. Hence, in order to detect the state of at least the main part of the material processed under predetermined operating conditions, a method is employed in which the concerned part of the cylinder assembly is divided longitudinally into blocks to visually observe or sample the contents therein. That is, in the case of the cylinder assembly as shown in FIG. 8 which is made up of the block cylinders which are coupled to one another with four tie bars, the cylinder assembly is disassembled into the block cylinders by removing the tie bars; and in the case of the cylinder assembly which is made up of the block cylinders which are coupled to one another through their flanges, the cylinder assembly is disassembled into the block cylinders by removing the bolts and nuts from the flanges. Thus, the operation of disassembling the cylinder assembly into the block cylinders takes a great deal of time and labor.
The cylinder assembly may be modified into one which is splittable along the central axis into an upper cylinder half and a lower cylinder half. However, such a modification is not practical in that the resultant cylinder assembly is high in manufacturing cost, and unsatisfactory in performance. In addition, since the cylinder assembly is large in total length, the flatness of the split surfaces of the upper and lower cylinder halves are adversely affected by thermal distortion, so that if the upper and lower cylinder halves become different in temperature, it is difficult for the split surfaces to be uniformly in contact with each other, and therefore the leakage of resin may occur. Similarly as in the above-described case, the operation of disassembling the cylinder assembly into the upper and lower cylinder halves take a great deal of time and labor. If the cylinder disassembling operation is not achieved within a short time, then for instance external heat adversely affects the performance of the extruder, making it impossible for the latter to operate in the same way again.
After the contents in the cylinder assembly are visually inspected or sampled, it is necessary to restore the cylinder assembly and to start the operation of the extruder. In order to prevent the molten resin material in the cylinder assembly from being cooled and solidified or from being changed in quality or deteriorated, it is essential to achieve the cylinder disassembling operation and the cylinder assembling operation within a short period of time.